2014 Vol. 39, No. 3
Objective In the first part of the paper we discuss the challenges of huge networks and multi-GNSS da-ta processing for the zero-difference(ZD)strategy.Using 4weeks’of data from global IGS GPS/GLONASS stations,we performed daily data processing with data sampling ranging from 5-15min.Acomparison of the processing time and product precision under different sampling data shows:①Computation efficiency is greatly improved by increasing data sampling;our results show the improve-ment of maximum 52%;② Difference of product precision was marginally observed,and product pre-cision is almost the same when the sampling rate was changed from 5-10min.To analyze the impact ofdifferent products on positioning applications,we performed PPP for 22globally distributed IGS sta-tions and kinematic precise orbit determination for GRACE satellites using products generated fromdifferent data sampling procedures.Results show:①Ｓｔａｔｉｃ ＰＰＰ ｐｒｅｃｉｓｉｏｎ ｄｉｆｆｅｒｓ ｂｙ ｌｅｓｓ ｔｈａｎ ２ｍｍand 6mm for the horizontal and height components,respectively;②ｋｉｎｅｍａｔｉｃ ＰＰＰ ｐｒｅｃｉｓｉｏｎ ｄｉｆｆｅｒｓby less than 1.5cm for each coordinate component and less than 2cm in three-dimensions.
Objective To improve the independent capacity of the halo orbit spacecraft,we propose an autonomousnavigation and control system based on the X-ray pulsar-based navigation(XNAV)principle.XNAVtheory is applied in the construction of a measurement equation.The full ephemeris dynamical modelis adopted in the establishment of the system state equation.We use the two-level differential correc-tion method to obtain a nominal halo orbit in the inertial coordinate system.Based on the differentialcorrection method,the halo orbit spacecraft is controlled using the navigation results from XNAV andthe small thrust propeller.A numerical simulation is carried out in the Earth-Moon L2halo orbit.Theresults demonstrate that the proposed method can accomplish autonomous navigation and control taskseffectively and the spacecraft can be maintained in the nominal orbit.
Objective The Chinese VLBI network(CVN)consists of four stations at Shanghai,Beijing,Kunmingand Urumqi,and are the VLBI tracking stations in the China’s Chang’e project.A solution schemewith the software OCCAM including the settings of parameters,the selection of models and the edi-tion of observations is introduced to analyze the astrometric and geodetic VLBI with experiments onthe four stations.Via a single session analysis and combined adjustment of single solutions,the coor-dinates and velocities for the Kunming and Beijing stations at the centimeter and millimeter per yearprecision are determined for the reference epoch J2000.0.Comparisons with the statistics from the a-dopted coordinates and velocities deduced in the Chang’e-1project show differences in coordinates ofup to 51.9cm,while the velocity varies up to 11.5mm/a,and are very significant.
Objective Computers may encounter the problem of numerical instability and output a wrong bit errorrate(BER)when decoding navigation satellite convolutional codes with the maximum a posterioriprobability(MAP)algorithm.Subsequently,this will affect the validity and the accuracy of the posi-tioning results.To address this problem,first a detailed analysis was executed.Based on this analy-sis,an improved MAP algorithm normalized with the maximum state metric is proposed,thus thequestion of numerical instability can be solved while still maintaining the original algorithm’s optimalperformance.Simulations further validate the effectiveness of this algorithm’s improvement.
Objective For in-orbit Beidou satellites,we make use of precise orbit for broadcast ephemeris SIS erroranalysis.We not only estimate SISURE,but also take correlation analysis and normality test.Through observational data of October 2012we find that the average SISURE is 1.45m;the R-TandT-N have low correlation,while among the other components are micro-correlation.We also find thatnearly all the SIS error components do not fit the normal distribution,and large errors can be detectedby kurtosis abnormal values,while systematic bias can be detected by skewness abnormal values.
Objective In this paper,we realize the ambiguity-fixing PPP using the integer clock product publishedby CNES.Ten globally distributed IGS tracking stations are processed.The results show that the ac-curacy of kinematic PPP with ambiguity fixing can achieve 1-2cm in the horizontal direction and a 3cm level for elevation;very attractive for the kinematic positioning applications.
Objective Considering the problem of estimating the location of wireless access points,an algorithm,using RSS-based ranging techniques,which does not need ranging model parameters,is proposed.Itfirstly eliminates the ranging model parameter related to the transmit power for the wireless accesspoint through the ratio relationships between the distances;and then it searches the best path loss in-dex based on the principle of least squares to determine the location of a wireless access point.Simula-tion results show that the algorithm can overcome the shortcomings of the existing location estimationalgorithms for wireless access points,and has better estimation accuracy.
Objective The separation of higher modes from multimode dispersion data is the key problem in Ray-leigh wave inversion.The complexity of energy distribution in real-world data leads to a difficulty inmode separation.This study developed a new method to confirm dispersion data using a forwardingwave-field.The results of numerical and real world experiments demonstrated that this method is ef-fective for confirming the dispersion data interpretation and improves dispersion extraction data quali-ty.
Objective By analyzing the high accuracy requirements of ZY-3image products and the key problems ingeometric processing,this paper proposes a production method for SC images based on virtual TDICCD array imaging technology.This method can be used to solve the geometrical registration problemin 4-bands multi-spectral image especially,since these adopt the same virtual TDI CCD array.Datacovering the Anping district,Hebei province,was used to produce the three-linear array and SC prod-uct,and to carry out adjustment experiments and precision analysis of the stereo model orientation.Experimental production was implemented to produce digital elevation models and digital orthographymaps,as well verify the precision of the products.Experimental results show that the geometric pre-cision of the SC product performs very well in the stereo mapping of 1∶50 000scale products.
Objective In this research,six MODIS L1Bdata of four consecutive days were normalized through pix-el-by-pixel atmospheric correction based on the 6S(second simulation of the satellite signal in the solarspectrum)radiative transfer model.Results show that the trend indicated by NDVI after normaliza-tion was different,and has better agreement with the phonological law,especially for pixels withdense vegetation.
Objective Based on the CA model of rill erosion,the research was focused on the effect of different si-zes of cells on the process and characteristic parameters of rill erosion on loess hillslopes as well as theavailability of a CA model through the Nash-Sutcliffe coefficient Ensand error coefficient Refor cumu-lative runoff and erosion.The results show:when other parameters of model and the running time areunchanged,if the size of cell becomes bigger,the process of rill erosion will accelerate,the averagewidth of the rill will get wider,the length will get longer,the trend of runoff and erosion will ad-vance,and at the same time,the cumulative runoff will decrease and the cumulative erosion will in-crease.If the size of cell becomes smaller,the effects will be reversed.In addition,the velocity of theCA model depends on the ratio of cell length and time step and the effectiveness of the model can beimproved when it is closed to overland flow velocity.
Objective An approach for merging geo-ontologies using description logics is proposed.The first stepin this method is to find the concepts and roles between two given ontologies.Then,the equivalentconcepts between two ontologies are provided as a starting point.Second,by combining direct withtransitive reasoning methods,we used reasoners(Pellet and SPARQLDL Java API)to detect semanticrelations(equivalence,subsumption,overlap and disjunction)between the concepts and roles of twoontologies including concepts vs.concepts,roles vs.roles,concepts vs.roles.Third,the conceptsand roles in the resource ontology are gradually merged into the target ontology.Finally,experimentsare conducted by combining fundamental geographic information and land use data for China.The re-sults indicate that the proposed method is feasible and valid for merging geo-ontologies.
Objective The paper analyses the concept and requirements for 4Dcadastre and proposes the spatio-temporal parcel concept.The evolutionary process of a spatio-temporal parcel is discussed and fourrights and interests transformations:identically equal,type,contraction and expansion and six spatialevolutions transformations:appearance,disappearance,boundary adjustment,union,split and re-al-location are proposed.Based on four spatial topological relationships and thirteen temporal topologicalrelationships,the spatio-temporal topological relationships of spatio-temporal parcel are established.Combining cadastral correlation theories and technical development,this paper describes a 4Dcadastre con-ceptual model which includes three solutions:tag pattern,hybrid pattern and the completely pattern.This re-search provides a theoretical reference and technical support for the establishment of 4Dcadastre.
Objective This paper presents a shape-based approach to extract arterial roads from urban road net-works is appropriate to the high level-of-detail found in volunteered geographic information(VGI)datasets.Firstly,the method calculates several shape descriptors of each polygon surrounded byroads.Secondly,some candidate arterial-road polygons are classified as seeds from all polygons withshape descriptors using support vector machine(SVM).Finally,based on seed polygons,a regionalgrowing method is proposed to connect the arterial-road features according to the Gestalt concept.Anexperiment shows that this method achieves good and effective arterial road extraction results,reflec-ting the constructed skeleton in urban network.Furthermore,a comparison analysis of high-levelroads attributes was also carried out to confirm the consistency between constructed road levels andour detected arterial roads.
Objective In this paper,we use the assortative coefficient to study the degree correlation of urbanstreet networks as represented by stroke intersections.It is found that some street networks demon-strate an assortative mixing pattern and others demonstrate disassortative mining pattern.The assor-tative networks would percolate easily and are resilient to breaks.This demonstrates potential forgeneral applicability to urban planning.Our conclusions are opposite to previous work and possiblereasons are discussed.
Objective Map patterns in building groups,as one of the essential foundations for cartographic gener-alization and multi-scale connection-relations,embodies the relationship of the material form of citiesto their social-economic functions.On the basis of related research at home and abroad,a multi-con-nected linear pattern is recognized taking advantage of parameter discrimination.With the analysis ofpattern organization laws,the structural parameters of linear patterns are characterized by distance,direction and size;then the neighborhood relationship was captured by proximity graph with the helpof a Delaunay triangulation;finally the multi-connected linear pattern is recognized by pruning theproximity graph,modeling the human processes.Experiments show that this approach is effective,feasible and practicable for multi-connected linear pattern recognition in agreement with cognitivecharacteristics.
Objective To solve the problem of poor calculating efficiency caused by mass data existed in tetrahedralgrowth algorithm,the concept of a separating-plane is introduced while a separating-plane theorem,and theorems for segment-plane and triangle-plane disjoint tests are established.By transforming thesegment-triangle disjoint test into the easier disjoint test between a separating-plane and triangle,alarge amount of triangles to be intersected with a segment are eliminated efficiently,greatly shorten-ing testing time.On the basis of the above theorems,a complete algorithm for a direct constrained-Delaunay tetrahedralization based on the boundaries of a polyhedron is presented.Experimental re-sults show that the algorithm runs stably and correctly,has a higher level of automation because ofless artificial intervention,and possesses higher efficiency compared with other similar algorithms.
Objective Aiming to solve the inconsistency between an input line and its reference lines,this paperproposes a method of snapping and adjusting input lines to unmovable reference lines.According tothe locations of the nodes on reference lines,auxiliary nodes are added to an input line.Both the origi-nal and added nodes on the input line within the tolerance distance to reference lines are then snappedto reference lines.Finally,the sequence of the snapped nodes on the input line is checked and adjustedso as to avoid self-intersection of the input line.Case studies showed that the inconsistency betweenthe input line and reference line was resolved for all the nodes in tolerance distance,and no self-inter-sections were found on the snapped lines.The proposed method is efficient for line level snapping,ap-plicable to integrate graphic data from different sources.
Objective One method for taking SLR as the global crustal vertical motion reference datum is proposedafter considering SLR ranging characteristics.The data for coordinates and velocity fields that SLR,GNSS and VLBI analysis centers submitted to the ITRF2008and ITRF2005was used to select highprecision co-location sites and calculate their vertical velocity field in the local coordinate system usingcoordinate conversion.Systematic errors between SLR and GNSS or VLBI vertical velocity field werecalculated based on a deduced mathematical model.With the calculated systematic errors,the verticalvelocity fields of GNSS and VLBI were corrected to the SLR vertical motion reference datum.TakingSLR as the global crustal vertical motion reference datum was proven to be feasible as the correlationcoefficient as the slope tends to be 1after consistency inspection.
Objective In regional crustal movement research,mathematical model is always used to estimate with-out observation the points which need attention.Then,we can build up a relatively even and meaning-ful regional crustal movement velocity field.In this paper we analyze the strengths and weaknesses ofthe common Euler and function models,and propose a new model with BP neural network based onEuler vector.This proposed model uses the geological properties of a Euler vector and the superiorityof BP neural network.It considers the various influences and uncertain information found in data pro-cessing.Therefore,the model can distinguish inner elastic strain from rigid-body of the plate.Theproposed model obtains precision through specimen verification.
Objective Focusing on the limitations of conventional methods,a new method for testing the stabilityof landslide monitoring network for long and narrow areas was studied.The process was divided intothree steps:Firstly,the relatively stability points were identified in the ITRF frame;Secondly,thereference points displacement was calculated in the local reference frame as defined by relatively stabilepoints;Thirdly,a displacement significance test was used to analyze the stability of these referencepoints.Using GPS observations(2008-2011)of a landslide monitoring network in the Three Gorgesreservoir area,the stability of all reference points was tested:finding moved reference points duringthree years of high water impoundment,with a horizontal displacement of the moved reference pointsof more than 4cm,with a maximum of 79.4cm.The displacement direction of unstable referencepoints was physically inspected along with the geographical environment,revealing that they wereconsistent with the results obtained from the proposed testing method.
Objective Existing steel bar counting methods based on image processing are not accurate and cannotadapt to steel bar diameter variation,or changes in the production process.This paper presents an au-tomatic steel bar counting method which makes use of an iterative Hough round transformation and amulti-threshold connectivity area.The algorithm first extracts ROI by morphological operations.Then,it scales the image size according to the diameter of the input steel bars to the standardizationdiameter size to accommodate the bars diameter change.Nest,an iterative Hough round transforma-tion is applied to the scaled ROI to extract steel bars.Finally,a multi-threshold connectivity areamethod is used to calculate the remaining bars.Experiments show that the algorithm can adapt to thesteel bar diameter changes and changes in the production process with high accuracy.